This invention relates to current sensors, and more particularly to corrected noncontacting current sensors which tend to be insensitive to transverse installation misalignment.
In systems including a large number of interconnected devices, any one of which is liable to fail, troubleshooting can be difficult. Various techniques are used to aid in locating defective components. In the context of discrete circuits using bipolar transistors or FETs, it was previously common to place a moderate-value resistor in series with the base or gate, so that a short-circuit from the emitter or collector, or the source or drain, respectively, to the base or gate, could be detected by noting the voltage across the resistor so added. The value of the resistor was selected so that its effect on the operation of the circuit was minuscule during normal operation of the device. With the increased usage of microcircuits, this simple approach has become less useful.
There are systems in which large numbers of generally identical electrical units are operated in parallel. These systems are ordinarily located in bays of large racks, where the packing density of the units makes access difficult. In such arrangements, it is desirable to individually monitor the current flow to each module, as for example by associating a current sensor with each module. Each current sensor may be as simple as, again, a series resistor through which the current to be monitored flows, and which generates a voltage attributable to the power supply current flow to the module. A gross failure of a module might be readily identifiable by the existence of a relatively large voltage across the series resistor.
A more subtle failure, such as that of a single component within the module, might be identifiable as a momentary surge of the supply current as the failed component draws excessive current and then fails in an open-circuited state. Monitoring for such failures may require that a running record be kept of the supply current of each module. However, when a gross defect is noted, such as might occur when someone enters a room filled with racks of such equipment, and smells an xe2x80x9celectrical firexe2x80x9d odor. Naturally, an immediate remedy is to cut all power to the equipment in the room. However, there is then the problem of tracking down the source of the odor. Since the odor vanishes shortly after the removal of power, and even were it present is not a good indicator of exact location, it may be difficult to locate the problem. In such an instance, it would be very valuable to have available a record of the moment-to-moment current in each module during the time in question, so as to be able to identify any current surges. With the use of microcircuits, mounted on printed-circuit boards, such a scheme would be quite possible, and might be relatively inexpensive to implement.
Naval and other ships contain large numbers of electrically driven motors, servos and the like, distributed throughout the various compartments of the ship. Many of these electrically driven devices could be styled as xe2x80x9cheavy machinery.xe2x80x9d The same problem as that described above, namely that of locating a defective device within numerous other devices in close quarters, exists in the shipboard context. However, the problem is not as easy to solve in the ship context, because the currents involved are too large for ordinary printed circuits to withstand. This, in turn, means that the mounting of current sensors cannot be accomplished by simply connecting a circuit board in-circuit with the current to be sensed or measured, but instead the current sensor must be custom-installed on or adjacent the large conductor. Such installations tend to be labor-intensive and therefore expensive, and additionally are subject to installation errors which may compromise the measurements.
Improved current measurement techniques are desired, as for example for fault monitoring.
An electrical current sensor arrangement according to a general aspect of the invention is for sensing the current in an elongated conductor. The arrangement comprises first and second current sensing devices which can be magnetically coupled to the current to be sensed, for generating sensed signals relating to the magnitude of the current being sensed. Each of the first and second current sensing devices has a preferred magnetic sensing axis, which in general is oriented relative to the current flow in the conductor so as to provide a signal. A nonmagnetic physical mounting is physically coupled to the first and second current sensors, for holding the first and second current sensors with their preferred sensing axes one of (a) parallel and (b) orthogonal, thereby defining a sensor plane in which the current sensing devices lie. The fact that the current sensing devices lie in the same plane necessitates or requires a spacing therebetween, which spacing remains fixed. The physical mounting is adapted for mounting adjacent an electrical conductor, with the sensor plane parallel with a tangent with an outer surface of the electrical conductor, and for, when so mounted, holding the preferred sensing axes of the sensors relative to the direction of current flow in the conductor so as to produce a sensed signal in at least one, and preferably both, of the current sensing devices, in response to current flow in the conductor. As a result, each of the current sensing devices senses magnetic fields related to less than the total current flowing through the electrical conductor, or at least gives an indication which is less than it would give if properly located and oriented. The arrangement includes electrical coupling means coupled to the first and second current sensors, for processing the sensed signals produced by the first and second current sensors, to thereby produce a signal representative of the total current in the electrical conductor. In one embodiment, the conductor has a generally circular cross-section. Ideally, the current sensors are corrected for at least one of (a) temperature effects and (b) unit-to-unit variation in sensitivity. In the version in which the sensing axes of the current sensors are parallel, a transverse separation of the sensors is desirable.
In one version of the arrangement according to an aspect of the invention, the electrical coupling means algebraically sums the currents represented by the signals generated by the first and second current sensing devices to produce the signal representative of total current in the electrical conductor.
According to another aspect of the invention, the physical mounting comprises a first physical mounting portion physically coupled to the first and second current sensors, for holding the first and second current sensors with their preferred sensing axes (a) parallel or (b) mutually orthogonal, thereby defining a sensor plane, and with a fixed or known spacing between the preferred sensing axes. According to this aspect of the invention, a second physical mounting portion is provided for mounting adjacent an electrical conductor. The second physical mounting portion includes means for holding the first physical mounting portion with the sensor plane parallel with a tangent with (or to) an outer surface of the electrical conductor, and for, when so mounted, holds the preferred sensing axes (a) generally parallel with the direction of current flow in the electrical conductor or (b) at 45xc2x0 to the direction of current flow. In one version of this aspect of the invention, the first physical mounting portion comprises a printed-circuit board, and the second physical mounting portion comprises a nonmagnetic structure including a printed circuit mounting portion defining a plane, and also including a depression shaped to the exterior of the conductor. The depression defines a longitudinal axis parallel with the plane of the printed circuit mounting portion.
In a kit of nonmagnetic mounting arrangements according to another avatar of the invention, each of the mounting arrangements includes first and second body arrangements. The first body arrangement defines
(a) a mounting location for a pair of current sensors, each defining a preferred magnetic sensing axis, for mounting the pair of current sensors thereon with a specific or fixed distance between the current sensors, and with the preferred sensing axes parallel so as to define a sensing plane;
(b) a circularly cylindrical cavity defining a longitudinal axis parallel with the preferred magnetic sensing axes of the current sensors and also defining a first radius, for mounting to a cylindrical electrical conductor having a radius substantially equal to the first radius, the longitudinal axis of the cavity being parallel with the preferred sensing axes, and the sensing plane orthogonal to a plane in which plural radii of the cavity lie.
The second body arrangement defines
(a) a second mounting location for a pair of current sensors, each defining a preferred magnetic sensing axis, for mounting the pair of current sensors thereon with the specific distance between the current sensors of the pair, and with the preferred sensing axes parallel so as to define a second sensing plane;
(b) a second circularly cylindrical cavity defining a second longitudinal axis parallel with the preferred magnetic sensing axes of the second pair of current sensors and also defining a second radius, different from the first radius, for mounting to a cylindrical electrical conductor having a radius substantially equal to the second radius, the longitudinal axis of the second cavity being parallel with the preferred sensing axes, and the second sensing plane orthogonal to a plane in which plural radii of the cavity lie.
Yet another embodiment of an avatar of the kit aspect of the invention lies in a kit of noncontacting magnetic sensors adapted for use with differing sizes of electrical conductors, where the kit comprises a first body arrangement. The first body arrangement defines
(a) a mounting location for a pair of current sensors, each defining a preferred magnetic sensing axis, for mounting the pair of current sensors thereon with a specific distance between the current sensors, and with the preferred sensing axes parallel so as to define a sensing plane;
(b) a circularly cylindrical cavity defining a longitudinal axis parallel with the preferred magnetic sensing axes of the current sensors and also defining a first radius, for mounting to a cylindrical electrical conductor having a radius substantially equal to the first radius, the longitudinal axis of the cavity being parallel with the preferred magnetic sensing axes, and the sensing plane orthogonal to a plane in which plural radii of the cavity lie.
This other embodiment also includes a second body arrangement, the second body arrangement defining
(a) a second mounting location for a pair of current sensors, each defining a preferred magnetic sensing axis, for mounting the pair of current sensors thereon with the specific distance between the current sensors of the pair, and with the preferred magnetic sensing axes parallel so as to define a second sensing plane;
(b) a second circularly cylindrical cavity defining a second longitudinal axis parallel with the preferred magnetic sensing axes of the second pair of corrected current sensors and also defining a second radius different from the first radius, for mounting to a cylindrical electrical conductor having a radius substantially equal to the second radius, the longitudinal axis of the second cavity being parallel with the preferred magnetic sensing axes, and the second sensing plane orthogonal to a plane in which plural radii of the cavity lie.
The kit also includes a pair of magnetically coupled current sensors, which are preferably corrected current sensors, each defining a preferred magnetic sensing axis, the pair of current sensors being dimensioned for mounting to any one of the first and second mounting locations of the first and second body arrangements, respectively.
A method for noncontact measurement of the current in a conductor according to another aspect of the invention includes the step of procuring two current sensors, preferably of the corrected type, each defining a preferred magnetic sensing axis. The current sensors are held with the preferred magnetic sensing axes mutually parallel and spaced apart from each other to define a sensor plane, and to also define a second plane parallel to the preferred magnetic sensing axes and orthogonal to the sensing plane. The sensor plane is held parallel to a tangent to an outer surface of a conductor through which current to be sensed flows, with the second plane approximately centered on the axis of the conductor. The magnetic fields about the conductor are sensed, to thereby produce current-representative signals from each of the current sensors. Finally, the current-representative signals from the two current sensors are summed to produce a signal representative of the actual current in the conductor.
In one mode of the method for noncontact measurement, the current to be sensed is an alternating current. In this mode, the step of procuring two current sensors includes the step of procuring two current sensors which respond to the absolute value of magnetic field, and the summing step includes the step of subtraction of one of the current-representative signals from the other. The processing can be performed in analog or digital form.
In accordance with another aspect of the invention, an apparatus for measuring current in a current-carrying conductor comprises a first current sensing device (preferably a corrected current sensing device) which can be magnetically coupled to the current to be sensed, for generating a sensed signal relating to the magnitude of the current being sensed. The first sensing device has a preferred magnetic sensing axis. A second current sensing device is included, which can be magnetically coupled to the current to be sensed, for generating a sensed signal relating to the magnitude of the current being sensed. The second current sensing device also has a preferred magnetic sensing axis. A nonmagnetic physical mounting is physically coupled to the first and second current sensors, for holding the first and second current sensors with their preferred magnetic sensing axes mutually orthogonal, thereby defining a sensor plane. The physical mounting is adapted for mounting adjacent an electrical conductor, with the sensor plane parallel with a tangent to an outer surface of the electrical conductor, for, when so mounted, holding the preferred magnetic sensing axes with a fixed angle between the direction of current flow in the electrical conductor and the preferred sensing axis of one of the first and second current sensors. An electrical coupling means or arrangement is coupled to the first and second current sensors, for processing the sensed signals produced by the first and second current sensors, to thereby produce a signal representative of the total current in the electrical conductor.
In one version of this apparatus, the electrical coupling means vectorially sums the currents represented by the signals generated by the first and second current sensing devices to produce the signal representative of total current in the electrical conductor. In a specific embodiment of this apparatus, the signals generated by the first and second current sensing devices are processed in accordance with the expression
{square root over (|S3|2+|S4|2)}={square root over (S2sin2(xcex8)+S2cos2(xcex8))}=S,
where "THgr" is the angle between total current S and sensed current components S3 and S4, to produce a signal representative of the total current in the electrical conductor.
In another version of an apparatus according to the other aspect of the invention, the apparatus comprises first and second (preferably corrected) magnetic sensors, each of which first and second magnetic sensors has a preferred magnetic sensing axis. A first mounting means is coupled to the first and second magnetic sensors, for holding the first magnetic sensor with its preferred magnetic sensing axis orthogonal with the preferred magnetic sensing axis of the second magnetic sensor, to thereby define a sensing plane. Second mounting means are coupled to the first mounting means and to the conductor, for mounting the first mounting means adjacent (juxtaposed to) the conductor, with the sensing plane generally parallel to a tangent to an outer surface of the conductor. A summing means or arrangement is coupled to the first and second magnetic sensors, for vectorially summing the current-representative signals of the first and second magnetic sensors, so as to compensate, or in such a fashion as to correct, yaw misalignment of the preferred magnetic sensing axes of the magnetic sensors. In a particularly advantageous embodiment, the summing means performs its summing according to the expression
{square root over (|S3|2+|S4|2)}={square root over (S2sin2(xcex8)+S2cos2(xcex8))}=S,
where S3 and S4 represent each sensor output, "THgr" the angle, and S the sum representing the total current.
In yet another version of the invention, a kit of nonmagnetic mounting arrangements is provided. Each of the mounting arrangements includes a first body arrangement, defining
(a) a mounting location for a pair of current sensors, each defining a preferred magnetic sensing axis, for mounting the pair of current sensors thereon with a fixed 45xc2x0 angle between the preferred magnetic sensing axes of the current sensors, to thereby define a sensing plane;
(b) a circularly cylindrical cavity defining a longitudinal axis lying parallel with a line lying in the sensing plane and making a fixed 45xc2x0 angle relative to the preferred magnetic sensing axes of the current sensors, and also defining a first radius, for mounting to a cylindrical electrical conductor having a radius substantially equal to the first radius, and with the sensing plane orthogonal to a plane parallel with the longitudinal axis; and
a second body arrangement, defining
(a) a mounting location for a pair of current sensors, each defining a preferred magnetic sensing axis, for mounting the pair of current sensors thereon with a fixed 45xc2x0 angle between the preferred magnetic sensing axes of the current sensors, to thereby define a sensing plane;
(b) a circularly cylindrical cavity defining a longitudinal axis lying parallel with a line lying in the sensing plane and making a fixed 45xc2x0 angle relative to the preferred magnetic sensing axes of the current sensors, and also defining a second radius different from the first radius, for mounting to a cylindrical electrical conductor having a radius substantially equal to the second radius, and with the sensing plane orthogonal to a plane parallel with the longitudinal axis.
Another kit of noncontacting magnetic sensors adapted for use with differing sizes of electrical conductors includes;
a first body arrangement, which first body arrangement defines
(a) a mounting location for a pair of current sensors, each defining a preferred magnetic sensing axis, for mounting the pair of current sensors thereon with a fixed 45xc2x0 angle between the preferred magnetic sensing axes of the current sensors, to thereby define a sensing plane;
(b) a circularly cylindrical cavity defining a longitudinal axis lying parallel with a line lying in the sensing plane and making a fixed 45xc2x0 angle relative to the preferred magnetic sensing axes of the current sensors, and also defining a first radius, for mounting to a cylindrical electrical conductor having a radius substantially equal to the first radius, and with the sensing plane orthogonal to a plane parallel with the longitudinal axis; and
a second body arrangement, which second body arrangement defines
(a) a mounting location for a pair of current sensors, each defining a preferred magnetic sensing axis, for mounting the pair of current sensors thereon with a fixed 45xc2x0 angle between the preferred magnetic sensing axes of the current sensors, to thereby define a sensing plane;
(b) a circularly cylindrical cavity defining a longitudinal axis lying parallel with a line lying in the sensing plane and making a fixed 45xc2x0 angle relative to the preferred magnetic sensing axes of the current sensors, and also defining a second radius different from the first radius, for mounting to a cylindrical electrical conductor having a radius substantially equal to the second radius, and with the sensing plane orthogonal to a plane parallel with the longitudinal axis
The kit also includes a pair of magnetically coupled current sensors, which are preferably corrected current sensors, each of which sensors defines a preferred magnetic sensing axis, where the pair of current sensors is dimensioned for mounting to any one of the first and second mounting locations of the first and second body arrangements, respectively.
A method for noncontact measurement of the current in a conductor according to a further manifestation of the invention includes the step of procuring two current sensors, each defining a preferred magnetic sensing axis, and holding the current sensors with their preferred magnetic sensing axes mutually orthogonal, to thereby define a sensor plane. The sensor plane is held parallel to a tangent to an outer surface of a conductor through which current to be sensed flows. The magnetic fields about the conductor are sensed by the current sensors, to thereby produce current-representative signals from each of the current sensors. The current-representative signals from the current sensors are processed to produce a signal representative of the actual or total current in the conductor. In a particular version of the method, the step of processing includes the step of calculating
{square root over (|S3|2+|S4|2)}={square root over (S2sin2(xcex8)+S2cos2(xcex8))}=S,
where S3 and S4 are signals representing the two sensor readings, S is the total current, and "THgr" the angle between the total current and S3.